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Muri seaweed problem highlights need for centralised wastewater system

The community has seen increased seaweed growth in the Muri Lagoon and poor lagoon health. A leading cause of the seaweed growth and the lagoon’s poor health is the excessive nutrients seeping into the ground water and sediments from on-site septic tanks. The Mei Te Vai Ki Te Vai project is working to provide a long term solution to this issue and seeking community support to identify suitable land for the wastewater treatment system.

The issue

In 2017-2018 the Mei Te Vai Ki Te Vai project team, Cook Islands Government ministries and experts conducted extensive environmental investigations to explore Muri Lagoon’s poor health.

These investigations found that nutrients from on-site wastewater systems (septic tanks) seeping into the ground water and sediments flow into the shallow parts of the lagoon. This is a leading cause of the lagoon’s poor health and resulting seaweed growth. Human activity, including disposal of grey water (used water from sinks, showers, baths, washing machines) in the sensitive Muri environment also contributes to the problem.

Some of these nutrients take years to reach the lagoon, so the sooner we stop using septic tanks and allowing nutrients to seep into the ground water in Muri, the sooner we will see improved health in the lagoon.

The solution

In order to restore the lagoon’s health long term, a reticulated (centrally operated) wastewater system is needed in Muri to treat and dispose of wastewater appropriately. This will significantly reduce the nutrients that are seeping into Muri Lagoon, causing the seaweed growth. In the years to follow, as the remaining nutrient source in the ground and lagoon sediment is released and slowly reduced, we will we see a reduction of seaweed in the Muri Lagoon.

Where are we now?

Following consultation with the community and key stakeholders we can confirm the preferred wastewater disposal option for Muri is land-based disposal. A draft design of a reticulated wastewater treatment system with the land-based disposal option has been prepared. The design includes biological treatment of wastewater, odour control to minimise impact on the surrounding community and landscaping to ensure the wastewater plant blends in with the surrounding environment.

Unfortunately, a number of challenges delayed this design being presented to the community in 2020. These challenges include the need to identify suitable land for the waste disposal site to allow land-based disposal to be a viable option.

In order to first ensure land-based disposal is a viable option, we need to identify two separate suitable packages of land; one for the wastewater treatment plant and another for the disposal site. Several offers of land have been received and currently being assessed. Not all land will be suitable for the disposal fields.

What type of land does the project need?

  • We need about 2 hectares (5 acres) of flat land for the treatment plant.

  • We also need 15 - 20 hectares (37 - 50 acres) of land for treated wastewater disposal.

  • This land must have the right soil types, be sloping, and not have environmental or cultural heritage value.

  • Ideally land for the disposal site should be outside of Muri. For example, in Avana and Turangi or nearby areas.

  • This land can be made up of smaller parcels of land, but each parcel must be at least 1 hectare (2.5 acres).

What can we do in the short term?

In the meantime, there are several things we all can do to help the lagoon recover:

  • Regularly maintaining existing septic tanks and plumbing to limit leaks and overflow to prevent nutrients entering the groundwater.

  • Planting around the streams to help reduce sediment and nutrients already in the ground ending up in the lagoon.

  • Avoiding draining and filling swamps.

  • Avoiding dumping of products such as insecticides, weed killer, pharmaceuticals, paint and motor oil onto the ground and using more eco-friendly alternatives.

It is important to note that even if we do all these things, the existing nutrients in the lagoon ecosystem means it will take some time for the Muri Lagoon to recover

Next steps

We need your help to find enough suitable land to progress with a land-based disposal wastewater system.

If you think you might have suitable land, please give us a call on +682 28851 or contact us via email at

If we are unable to identify suitable land for both the treatment plant and disposal site, the project may need to consider alternative solutions such as an ocean outfall disposal method.

More information can be found on our project website:

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